Yes, we (at https://codeable.io) use Trello for pretty much all internal (async) communications, from Sprints (user stories) to features, to ideas,...

No learning curve, exactly the right features.

And also there's something I like in Trello that Basecamp (I know comparing apples to oranges, but both can be used for similar purposes) doesn't support: closure. When something is no longer relevant, you archive it and it's gone, no more mental burden. Quite important when you have 100s of tickets.